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→Life Cycle
[[Image:Balantidium pig trophozoite.jpg|thumb|right|150px|''Balantidium'' trophozoite from a pig - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
[[Image:Balantidium pig trophozoite.jpg|thumb|right|150px|''Balantidium'' trophozoite from a pig - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
*Most protzoal reproduction is asexual using binary fission, schizogony and sporogony
*Most protozoal reproduction is asexual via binary fission, schizogony and sporogony
*Some protozoa also use sexual reproduction called gametogony
*Some protozoa also use sexual reproduction called gametogony
*In some species, sexual and asexual reproduction occurs in the same host, whilst in others asexual reproduction occurs in the vertebrate host and sexual reproduction in the arthropod vector
*In some species, sexual and asexual reproduction occurs in the same host, whilst in others asexual reproduction occurs in the vertebrate host and sexual reproduction in the arthropod vector
*Homogenous
*Homoxenous
**Parasite uses a single host species during its life cycle (direct)
**Parasite uses a single host species during its life cycle (direct)
**E.g. ''Eimeria''
**E.g. ''Eimeria''
**Sporozoites feed and grow
**Sporozoites feed and grow
*As the sporozoites grow the nucleus divides forming a '''schizont'''
*As the sporozoite grows the nucleus divides forming a '''schizont'''
*The schizont contains numerous elongated '''merozoites'''
*The schizont contains numerous elongated '''merozoites'''
*The formation of merozoites is the first asexual reproductive stage called '''schizogony'''
*The formation of merozoites is the first asexual reproductive stage called '''schizogony'''
*The schozont ruptures releasing the merozoites which also invade the epithelial cells
*The schizont ruptures releasing the merozoites which also invade the epithelial cells
*Another generation of schizonts form which is the beginning of the sexual phase of reproduction called '''gametogeny'''
*Another generation of schizonts form which is the beginning of the sexual phase of reproduction called '''gametogony'''
*The merozoites form male '''microgamonts''' or female '''macrogamonts'''
*The merozoites form male '''microgamonts''' or female '''macrogamonts'''
**Collectively known as gamonts or gametocytes
**Collectively known as gamonts or gametocytes
*The microgamonts released from the microgametocyte penetrate and fertilise the macrogamete (which is contained within the macrogametocyte)
*The microgamonts released from the microgametocyte penetrate and fertilise the macrogamont (which is contained within the macrogametocyte)
*Gametogeny forms the '''zygote'''
*Gametogony forms the '''zygote'''
**Surrounded by a cyst wall
**Surrounded by a cyst wall
**Forms the '''oocyst'''
**Forms the '''oocyst'''
*The oocyst is passed in the faeces as unsporulated
*The oocyst is passed in the faeces and is unsporulated
*The oocyst becomes sporulated in the second asexual reproductive phase called '''sporogeny'''
*The oocyst becomes sporulated in the second asexual reproductive phase called '''sporogony'''
*Once the oocyst is sporulated it is infective
*Once the oocyst is sporulated it is infective